Maintenance-free respirators (sometimes referred to as “filtering face masks” or “filtering face pieces”) are commonly worn over the breathing passages of a person to prevent impurities or contaminants from being inhaled by the wearer. Maintenance-free respirators typically comprise a mask body and a harness and have the filter material incorporated into the mask body itself—as opposed to having attachable filter cartridges or insert molded filter elements (see e.g., U.S. Pat. No. 4,790,306 to Braun)—to remove the contaminants from the ambient air.
To ensure that contaminants do not inadvertently enter the mask interior without passing through the filter media, maintenance-free respirators have been designed to fit snugly upon the wearer's face. Conventional maintenance-free respirators can, for the most part, match the contour of a person's face over the cheeks and chin. In the nose region, however, there is a complex contour change, which makes a snug fit more challenging to achieve. Failure to achieve a snug fit can allow air to enter or exit the respirator interior without passing through the filter media. In this situation, contaminants may enter the wearer's breathing track, and other persons or things may be exposed to contaminants exhaled by the wearer. Further, the wearer's eyewear can become fogged, which, of course, makes visibility more troublesome to the wearer and creates further unsafe conditions for the user and others.
Nose clips are commonly used on maintenance-free respirators to prevent fogging of a wearer's eyewear. Conventional nose clips are in the form of malleable, linear, strips of aluminum—see, for example, U.S. Pat. Nos. 5,307,796, 4,600,002, 3,603,315; see also U.K. Patent Application GB 2,103,491 A. More recent products use an “M” shaped band of malleable metal to improve fit in the nose area—see U.S. Pat. Nos. 5,558,089 and Des. 412,573 to Castiglione—or spring loaded and deformable plastics—see U.S. Patent Publication 2007/0044803A1 and application Ser. No. 11/236,283. Nose foams are also regularly used on the top section of the mask to improve fit and to prevent eyewear fogging—see U.S. patent application Ser. Nos. 11/553,082 and 11/459,949. Although nose clips and nose foams may assist in providing a snug fit over the wearer's nose to preclude eyewear fogging problems, the risk still exists that the wearer's eyewear could become fogged from air that leaves the mask interior through the mask body. That is, the eyewear may become fogged—even though the mask properly fits the wearer's face in the nose region—by warm, moist exhaled air that is forced through the mask body in the sinus region.
Persons skilled in the art of developing maintenance-free respirators have therefore taken other measures to preclude eyewear fogging caused by air that is rightfully purged from the mask interior through the mask body. Examples of some of these developments are disclosed in the following Japanese patents publications: 2005-13492, 92-39050, 2003-236000, 2001-161843, 2001-204833, 2003-236000, 2005-13492, 2001-161843, Hei 9-239050, and in U.S. Pat. No. 6,520,181. In these developments—like the nose clip and nose foam features cited above—an additional item is added to the sinus region of the mask body to prevent exhaled air from passing through this portion of the respirator. Although the prior art has addressed the need for precluding eyewear fogging, it has not done so in a manner that uses existing mask body components to address the problem.